Water treatment apparatus incorporating walnut shell filter media and a draft tube system

ABSTRACT

The present invention relates generally to a system and method for treating wastewater in a filter media apparatus having a draft tube system. The filter media may be walnut shell media.

RELATED APPLICATIONS

This application claims the benefit under 35 U.S.C. §120 as acontinuation of U.S. application Ser. No. 13/119,497 titled “WATERFILTER APPARATUS INCORPORATING WALNUT SHELL FILTER MEDIA AND A DRAFTTUBE SYSTEM,” filed on Mar. 17, 2011, now U.S. Pat. No. 8,747,667, as anational stage entry under 35 U.S.C. §371 of PCT applicationPCT/US2009/058005, titled “WATER TREATMENT APPARATUS AND SYSTEM,” filedSep. 23, 2009, which claims the benefit under 35 U.S.C. §119(e) to U.S.Provisional Application Ser. No. 61/099,604, titled “PULSED BACKWASH FORWALNUT SHELL FILTER,” filed on Sep. 24, 2008; and U.S. ProvisionalApplication Ser. No. 61/099,600, titled “PULSED AIR WALNUT SHELLFILTER,” filed on Sep. 24, 2008; and U.S. Provisional Application Ser.No. 61/099,597, titled “WALNUT SHELL FILTER PROCESS,” filed on Sep. 24,2008; and U.S. Provisional Application Ser. No. 61/175,579, titled “TUBEDESIGN AND PROCEDURE FOR WALNUT SHELL FILTER,” filed on May 5, 2009,each of which are incorporated by reference in their entireties for allpurposes.

BACKGROUND OF INVENTION

Field of Invention

The present invention relates to a system and method for treatingwastewater, and more particularly to a wastewater treatment system andmethod utilizing a walnut shell filter media.

Discussion of Related Art

Walnut shell filter media is known for its affinity for both water andoil, making it a desirable filter media and is typically used for theremoval of oil from water and wastewater. Conventional walnut shellfilters include pressurized deep bed applications in which the water isforced through a bed depth. Periodic backwashes are also routinelyconducted to regenerate the bed. Typical backwash methods includeexpanding or turning the bed by imparting energy to the bed.

Conventional backwash systems include mechanical mixing and mechanicalscrubbing with impellors and recycle lines, as well as the introductionof high velocity gas or high velocity water in a countercurrentdirection. Mechanical systems used to backwash beds increase the initialcosts of the system and may lead to increased maintenance costs toservice mechanical seals. Recirculation of the bed also increases theinitial and maintenance costs of the filter unit and increases thefootprint of the filter unit with additional pumps for recirculation.The mechanical backwash methods also utilize backwash fluid to removeany oil and suspended solids released from the bed, which leads to thegeneration of significant amounts of backwash fluid. Similarly, the useof high velocity backwash liquid generates a large volume of backwashfluid. Conventional backwash systems are also known to create dead spotsin which the filter media is not sufficiently turned and/or in which thebackwash fluid does not reach, effectively leaving oil and suspendedsolids in the bed.

A need remains for a compact walnut shell filter media unit having afootprint sufficiently small to be used in offshore applications.Moreover, there is a need to reduce the amount of backwash watergenerated during backwash of the walnut shell filter unit and to reducethe number of dead spots which are not contacted by the backwash fluid.

SUMMARY OF INVENTION

In accordance with one or more embodiments, the invention relates to asystem and method of treating wastewater.

In one embodiment, a filter apparatus having a vessel, a walnut shellfilter media positioned in the vessel and a feed inlet positioned in thevessel above the filter media. The filter apparatus may have a drafttube system positioned in the filter media which may be constructed andarranged to substantially roll the filter media. The filter apparatusmay also have a first fluid inlet constructed and arranged to deliver afirst fluid to the draft tube system and a filtrate outlet positionedbelow the filter media.

Another embodiment is directed to a system for filtering wastewater. Thesystem includes a source of wastewater comprising oil and suspendedsolids and a plurality of filter units. Each filter unit includes avessel, a walnut shell filter media positioned in the vessel and a feedinlet positioned in the filter media and fluidly connected to the sourceof wastewater. The filter unit also includes a draft tube systempositioned in the filter media constructed and arranged to substantiallyroll the filter media, a first fluid inlet constructed and arranged todeliver a first fluid to the draft tube system, and a filtrate outletpositioned below the filter media. The filter unit also includes acontroller in communication with the feed inlet of each of the pluralityfilter units; the controller configured to generate a first controlsignal that initiates flow of wastewater to the feed inlet of a first ofthe plurality of filter units, and to generate a second control signalthat interrupts flow of wastewater to the feed inlet of a second of theplurality of filter units.

Another embodiment is directed to a method of filtering a contaminatedliquid comprising oil and suspended solids utilizing a filter apparatushaving a vessel, a walnut shell filter media positioned in the vesseland a feed inlet positioned in the vessel above the filter media. Thefilter apparatus may have a draft tube system positioned in the filtermedia which may be constructed and arranged to substantially roll thefilter media. The filter apparatus may also have a first fluid inletconstructed and arranged to deliver a first fluid to the draft tubesystem and a filtrate outlet positioned below the filter media.

Other advantages, novel features and objects of the invention willbecome apparent from the following detailed description of the inventionwhen considered in conjunction with the accompanying drawings, which areschematic and are not intended to be drawn to scale. In the figures,each identical or substantially similar component is represented by asingle numeral or notation. For purposes of clarity, not every componentis labeled in every figure, nor is every component of each embodiment ofthe invention shown where illustration is not necessary to allow thoseof ordinary skill in the art to understand the invention.

BRIEF DESCRIPTION OF DRAWINGS

The accompanying drawings are not intended to be drawn to scale. In thedrawings, each identical or nearly identical component that isillustrated in various figures is represented by a like numeral. Forpurposes of clarity, not every component may be labeled in everydrawing. In the drawings:

FIG. 1 is a schematic drawing of a filter apparatus according to one ormore aspects of the invention;

FIG. 2a is a schematic drawing showing one aspect of the operation of afilter apparatus;

FIG. 2b is a schematic drawing showing an aspect of the operation of thefilter apparatus of 2 a;

FIG. 2c is a schematic drawing showing an aspect of the operation of thefilter apparatus of 2 b;

FIG. 3 is a cross-sectional schematic plan view of a filter vesselaccording to one or more embodiments of the invention;

FIG. 4 is a schematic drawing showing a filter apparatus according toone or more aspects of the invention;

FIG. 5 is an elevated schematic side view of a draft tube base portionaccording to one or more aspects of the invention;

FIG. 6 is a block diagram showing a filter system according to one ormore aspects of the invention;

FIG. 7 is a graph showing the total outlet oil concentration verses timeaccording to one or more aspects of the invention; and

FIG. 8 is a flow chart of one embodiment of the invention.

DETAILED DESCRIPTION

The invention is directed to wastewater treatment systems utilizing afilter media bed. “Wastewater,” as used herein, defines any wastewaterto be treated such as surface water, ground water, a stream ofwastewater from industrial and municipal sources, having contaminantssuch as oil and/or suspended solids, and includes produced water fromprimary or secondary treatment systems.

One embodiment of the present invention includes a filter apparatuscomprising a vessel containing a filter media. The vessel may be open tothe atmosphere or closed to operate under pressure. The vessel may besized and shaped according to a desired application and volume ofwastewater to be treated to provide a desired throughput and/or adesired period of operation before a backwash is initiated. The vesselmay have any bed depth desired based upon the desired volume ofwastewater to be treated and the filter media selected for theparticular application. Accordingly, the vessel may have any bed depthof filter media, such as a shallow bed of about 10 inches up to a deepbed of about 66 inches or more. The filter vessel may be constructed ofany material suitable for a particular purpose. For example, an openfilter vessel may be an open tank formed of cement. In one embodiment, aclosed filter vessel may be formed of coated carbon steel, stainlesssteel, or fiberglass reinforced polymer.

Any filter media suitable for removal of the target contaminant orcontaminants may be used so long as it is also suitable for use in afilter bed. One filter media useful in removing oil and suspended solidsfrom wastewater is walnut shell filter media, such as media made fromEnglish walnut shells and black walnut shells.

One embodiment of the filter apparatus includes a vessel having one ormore sidewalls depending upon the desired shape of the vessel. Forexample a cylindrical vessel may have one sidewall while a square orrectangular vessel may have four side walls. In one embodiment, thevessel has a cylindrical shape having one continuous sidewall positionedbetween the first and second walls. In one embodiment, the vessel isclosed wherein the one or more sidewalls extend between a first wall anda second wall.

The filter media may be positioned in the vessel at a pre-selected depthand may fill the entire volume of the vessel or be contained in aparticular portion of the vessel. For example, a portion of the volumeof the vessel adjacent the first wall and/or the second wall may be freeof filter media. Filter media may be contained within the vessel by oneor more dividers, such as screens or perforated plates, which retain thefilter media in a desired location within the vessel while allowingwastewater to flow throughout the media in the vessel.

In some embodiments, the filter apparatus includes a draft tube system.The draft tube system may be constructed and arranged to intermittentlybackwash the filter media by providing a desired volume and/or velocityof backwash fluid to roll the bed. As used herein, “rolling the bed” isdefined as the movement of the filter media during backwash in which thefilter media at or near the second wall of the vessel is partially orcompletely moved through the draft tube system toward the first wall ofthe vessel and back toward the second wall of the vessel. The draft tubesystem may be sized and shaped for a desired application and volume offilter media to be backwashed and/or to operate within a preselectedtime period for backwash operation. The draft tube system may compriseone or more draft tubes positioned in the media. As used herein, a“draft tube” is a structure having one or more sidewalls open at bothends which when positioned in the filter media provides a passageway forflow of filter media during backwash. In one embodiment, the vessel mayhave a volume filter media of about 3 to about 6 times the volume of adraft tube or the summation of the volumes of the draft tubes in thedraft tube system.

The draft tube may be constructed of any material suitable for aparticular purpose as long as it is abrasion and oil resistant. Forexample, the draft tube may be formed of the same material as the vesselor may be formed of other lighter and less expensive materials, such asplastics, including fiberglass reinforced plastics. The draft tube maybe preformed for insertion into the vessel or manufactured as part ofthe vessel. As such, the draft tube may be designed to retrofit currentfilter media units. The draft tube system may be supported on the secondwall of the vessel. Alternatively, the draft tube system may besupported on a divider or media retention plate, such as a screen orperforated plate, designed to retain the media within a region of thevessel while allowing the flow of liquid and contaminants into and outof the media.

An individual draft tube may be sized and shaped according to a desiredapplication and volume filter media to be backwashed and/or to operatewithin a preselected time period for backwash operation. The draft tubemay also be sized and shaped to provide a desired level of agitationwithin the draft tube to partially or completely scrub the filter mediathereby releasing at least a portion of the oil and suspended solidsfrom the filter media. The desired draft tube system volume may beprovided by a single draft tube or by multiple draft tubes having atotal volume substantially equal to the desired volume. An individualdraft tube may have a cross sectional area of any shape, such ascircular, elliptical, square, rectangle, or any irregular shape. Theindividual draft tube may have any overall shape, such as conical,rectangular and cylindrical. In one embodiment, the draft tube is acylinder. The draft tube may be positioned in the filter media so as tobe entirely enveloped by the filter media as well as to be entirelyfilled with the filter media. One or both ends of the draft tube may beconstructed and arranged to assist flow of filter media into and/or outof the draft tube. For example, the side wall at a first end of thedraft tube may include one or more cut outs forming passageways to allowsome of the filter media at or near the first end of the draft tube toenter through the sidewall of the draft tube. The cutouts forming thepassageways may have any shape to allow a sufficient volume of filtermedia to enter the draft tube. For example, cut outs may be triangular,square, semicircular or have an irregular shape. Multiple passagewaysmay be identical to one another and uniformly positioned about the firstend of the draft tube to equally distribute flow of filter media in thedraft tube.

The draft tube or draft tubes may be positioned at any suitable locationwithin the filter media. For example, a single draft tube may, but neednot be positioned centrally in relation to the vessel sidewalls.Similarly, multiple draft tubes in a single vessel may be randomlypositioned or positioned in a uniform pattern in relation to the vesselsidewalls. In one embodiment, a single draft tube is positioned in thefilter media in relation to the vessel so that an axis extending fromeach end of the draft tube is co-axial with an axis parallel to thesidewall of the vessel. Multiple draft tubes in a single vessel may, butneed not be identical in volume or cross sectional area. For example, asingle vessel may comprise cylindrical, conical and rectangular drafttubes of varying height and cross sectional area. In one embodiment, avessel may have a first draft tube centrally positioned having a firstcross sectional area and a plurality of second draft tubes positionedadjacent the side wall of vessel in which each of the second draft tubeshas a second cross sectional area smaller than the first cross sectionalarea. In another embodiment, a vessel has a plurality of identical drafttubes.

In another embodiment, the draft tube may include a baffle to prevent orreduce backflow within the draft tube. The baffle may have any size andshape suitable for a particular draft tube. For example the baffle maybe a plate suitably positioned on an inner surface of the draft tube ora cylinder positioned in the draft tube. In one embodiment, the bafflemay be a solid or hollow cylinder centrally positioned within the drafttube.

The filter media vessel also includes a wastewater feed inlet positionedabove the filter media and a filtrate outlet positioned below the filtermedia. The vessel also includes a first inlet for a first fluidconstructed and arranged to deliver the first fluid to a first end ofthe draft tube to induce during backwash a flow of the filter mediawithin the draft tube from the first end of the draft tube to the secondend of the draft tube while inducing flow of the filter media along anoutside sidewall of the draft tube from the second end of the draft tubeto the first end of the draft tube.

Operation of the draft tube system during backwashing establishescountercurrent flows within the vessel and causes the filter media tomove as exemplarily shown in filter media apparatus 100 in FIG. 1. Thefilter media 16 moves from the first end 12 of the vessel 20 along theoutside of the draft tube 18 to the second end 14 of the vessel 20 whereit may then enter the first end 22 of the draft tube 18 adjacent thesecond end 14 of the vessel 20 as shown by the dashed flow lines (notlabeled). The filter media 16 (shown only in part) then moves within thedraft tube 18 in inner region 50 from the first end 22 of the draft tubeto the second end 24 of the draft tube where it exits the tube andenters a peripheral zone 26 of the vessel 20 as shown by the dashed flowlines (not labeled). As used herein, a “peripheral zone” is an internalvolume of the vessel not occupied by the draft tube system. Whileflowing in the draft tube 18, the filter media 16 may mix therebyreleasing a portion of the oil and suspended solids previouslyimmobilized on the filter media. During backwash, upon exiting the drafttube and entering the peripheral zone, the filter media is in aturbulent zone above the draft tube in which the filter media continuesto mix releasing additional contaminants, such as oil and suspendedsolids. Filter media 16 is represented in the figures as uniformspherical particles, however, it is understood that the filter media maybe comprised of any particle size and shape, including irregularlyshaped particles.

The first fluid may be any fluid to induce movement of the filter mediathrough the draft tube. For example the first fluid may be a gas, suchas air or a produced gas; a liquid, such as the filtrate or wastewaterto be filtered; and combinations thereof. In one embodiment, the firstfluid is a gas. Although the first fluid inlet is shown below the filtermedia, in other embodiments, the first fluid inlet may be positionedwithin the draft tube 18. The first fluid inlet may comprise one or moreinlets positioned within the vessel to deliver the first fluid to thedraft tube system to impart flow of the filter media through the drafttube system. The first fluid inlet may have any configuration suitablefor delivering the first fluid to the draft tube. For example, the firstfluid inlet may be an orifice, a nozzle, or a jet for delivering a gas,liquid, or combination thereof to the draft tube. In one embodiment thefirst inlet is a diffuser for delivering the gas to the draft tube.

The filter vessel may also include one or more second inlets to delivera second fluid to a peripheral zone. The second inlets may deliver thesecond fluid at or near the second wall of the vessel to induce flow orassist in the flow of media towards the first end of the draft tube. Oneor more second fluid inlets may be positioned within the vessel toprovide backwash flow to the vessel and direct filter media toward thedraft tube system. The second fluid may be a gas, a liquid, such as thefiltrate or wastewater to be filtered, and combinations thereof. In oneembodiment, the second fluid is the wastewater diverted from thewastewater feed inlet or be diverted from the filtrate outlet. Thesecond fluid inlet may have any configuration suitable for deliveringthe second fluid to the peripheral zone. For example the second fluidinlet may be an orifice, a nozzle, or a jet for delivering a gas,liquid, or combination thereof. In one embodiment, the second inletextends into the peripheral zone. The second inlet may extend from anysuitable location to assist in water distribution. For example, thesecond inlet may extend into the peripheral zone from the vessel sidewall and/or from the draft tube sidewall. In another embodiment, thesecond inlet may extend into the peripheral zone at an angle having acomponent tangential to the side wall of the vessel.

In yet another embodiment, the peripheral zone may also include one ormore first fluid inlets to further agitate the filter media bed. Thefirst fluid inlets in the peripheral zone may, but need not, beidentical to the first fluid inlet constructed and arranged to deliverthe first fluid to the draft tube.

The peripheral zone of the vessel may also include a scrub zone locatedabove the second end of the draft tube. The filter media exiting thedraft tube may be further mixed thereby releasing additional oil andsuspended solids from the filter media during the backwash cycle.

In one embodiment, upon completion of a backwash cycle, setting of thebed may be aided with the introduction of a gas, such as air or producedgas, through the draft tube system to disturb the media sufficiently toallow resettling. The gas may be introduced intermittently during thebed setting stage. The bed may be allowed to settle by gravity betweenpulses of gas.

Intermittent pulsing of the gas may also coincide with or alternate withintermittent pulsing of liquid through the second fluid inlet. Pulsingbursts of gas and liquid may disturb the bed sufficiently to allow thebed to compact thereby reducing void space and overall bed volume whencompared to conventional bed setting techniques. Typically afterbackwashing, filter media beds are set by gravity and feed forward flowof wastewater, which may result in insufficient set of the media andinefficiencies in which the wastewater short circuits or channels in thefilter media and breakthrough of oil and suspended solids.

Another embodiment is directed to a wastewater treatment systemincluding a plurality of filter media units to provide continuousfiltration while one or more filter media units are off line because ofoperating in a backwash cycle or bed setting stage. In the wastewatertreatment system, a source of wastewater including at least onecontaminant may be fed in parallel to a plurality of media filter units.Wastewater feed flow to one of the filter media units may be interruptedwhile wastewater feed flow to the remaining filter media unitscontinues. The filter media unit taken offline may then be backwashedand have its bed set before being brought back into service. Once thefilter media unit is brought back into service, another of the filtermedia units may be taken out of service for the backwashing and bedsetting cycles.

In some embodiments, the system and/or individual filter media apparatusmay include a controller to interrupt and initiate flows as desired. Asused herein, the term “interrupt” is defined as complete cessation offlow. A controller may direct the flow of the wastewater feed, the firstand second fluids and the gas depending upon the desired operatingconditions for the apparatus. The controller may adjust or regulatevalves associated with each potential flow based upon signals generatedby sensors positioned within the apparatus. For example, a sensor maygenerate a first signal indicating the pressure drop over the filtermedia bed has reached a predetermined value thereby triggering thecontroller to interrupt flow of the wastewater at the feed inlet and toinitiate flow of the wastewater through the second fluid inlet and gasthrough the first fluid inlet. Similarly, the controller can initiatebackwash based upon a second signal generated by the passage of apredetermined period of time. The controller may also generate a controlsignal interrupting wastewater feed to one filter media apparatus andinitiating flow of wastewater feed to another filter media apparatusbased upon the first signal, the second signal, and combinationsthereof.

Another embodiment is shown in FIG. 2a . Apparatus 200 comprises acylindrical vessel 20 having a side wall 40, a first wall 42, and asecond wall 44. A filter media 16 is contained within a portion of thevessel 20 with media retention plate 30 positioned adjacent the firstend 12 of the vessel and screen 60 positioned adjacent the second end 14of the vessel. Media retention plate may have any structure suitable,such as a screen or a perforated plate to retain the filter media withina portion of the vessel while allowing the feed liquid and contaminantsto pass into and out of the media. Vessel 20 also comprises a first end12 adjacent the first wall 42, a second end 14 adjacent the second wall44, and a wastewater feed inlet 32 adjacent the first end 12 of thevessel 20 and above the filter media 16. In FIG. 2a , vessel 20 alsoincludes a filtrate outlet 38 positioned below the filter media 16adjacent the second end 14 of the vessel 20.

In FIG. 2a , a cylindrical draft tube 18 having a first end 22 and asecond end 24 is centrally positioned within the filter media 16 suchthat the first end 22 of the draft tube 18 is adjacent the second end 14of the vessel. Filter media 16 is also positioned within draft tube 18,and is shown in part in FIG. 2a . The second end 24 of the draft tube ispositioned sufficiently below an upper end of the filter media bed sothat sufficient filter media is present in the bed to refill the drafttube upon completion of a backwash cycle. A peripheral zone 26 in vessel20 is a region delineated by the volume of the filter media 16 excludingthe space occupied by the filter media in the draft tube 18. A scrubzone 28 in the peripheral zone is positioned above a top surface of themedia, between the top surface of the media and a screen 30. Screen 30is positioned above the scrub zone 28 adjacent the first end 12 of thevessel 20 to prevent loss of media during backwash. Also shown in FIG.2a is scrub zone 28 in the peripheral zone positioned between an uppersurface of the filter media bed 54 and a lower surface of the screen 30.FIG. 2a shows screen 30 though it is understood that any device orstructure that maintains the media in the vessel may be used. Forexample, the media may be retained by a perforated plate or cylinder aswell as a cylindrical screen. A first fluid inlet 34 is constructed andarranged to provide a first fluid to the draft tube. In FIG. 2a , afirst fluid inlet 34 includes an air diffuser 46. Second fluid inlet 36is constructed and arranged to deliver the second fluid to theperipheral zone adjacent the second end of vessel 20. The vessel 20 inFIG. 2a includes contaminant outlet 50 for removing contaminants such asoil and suspended solids from the vessel. Optionally, the peripheralzone may comprise one or more first fluid inlets to partially roll thebed during filtration and/or to assist in expanding and rolling the bedduring backwash.

During filtration, wastewater containing oil and suspended solids isdirected to feed inlet 32, passes through screen 30 and enters thefilter media 16 in the bed adjacent the first end 12 of the vessel 20towards the second end 14 as noted by dashed flow arrows in FIG. 2a .Wastewater simultaneously passes through the filter media 16 in thedraft tube 18 from the second end 24 of the draft tube to the first end22 of the draft tube. Filtrate exits the vessel 20 via filtrate exit 38and may be directed to further treatment or discharged.

To extend the period of time in which filtration occurs betweenbackwashes, the first fluid may be pulsed to the draft tube via firstfluid inlet 34 during the filtration cycle. Optionally, the first fluidmay be pulsed via one or more first fluid inlets (not shown) positionedin the peripheral zone during filtration. As used herein, a “pulsedflow” is defined as a flow of fluid which is intermittently interrupted.A pulsed flow may occur at random intervals or may be periodic, in thatthe flow regularly cycles between off and on at preselected intervals.The period of time in which the fluid flows may, but need not be thesame as the period of time in which the fluid flow is interrupted. Forexample, the fluid may flow for a longer or shorter period of time thanthe period of time in which fluid flow is interrupted. In oneembodiment, the period of time in which the fluid flows is substantiallyidentical to the period of time in which fluid flow is interrupted.Pulsing the first fluid, such as a gas, may partially turn the bed offilter media thereby reducing the pressure drop and extending the runtime between backwash cycles. Extending the filtration run time betweenbackwash cycles may reduce the overall number of backwashes therebyreducing the volume of backwash generated during the life of the filterapparatus.

Filtration continues through filter media 16 until it is desirable toclean the filter media by backwashing the filter media. In oneembodiment, backwash may be initiated when the pressure drop across thefilter media reaches a predetermined value or when the vessel has beenin service for a predetermined time.

As shown in FIG. 2b , upon initiating a backwash, wastewater flow tofeed inlet 32 and flow of the filtrate from the filtrate outlet areinterrupted. Flow of gas is initiated through first fluid inlet 34 anddiffuser 46 and flow of the wastewater is initiated though second fluidinlet 36. In one embodiment, the flow of the second fluid may occur viaa filtrate outlet thereby eliminating a separate inlet for the secondfluid. Flow of the gas through first fluid inlet 34 may, but need not,occur before the flow of the second fluid is initialized. In oneembodiment the flow of the first and second fluids beginssimultaneously, while in another embodiment the flow of the second fluidbegins before flow of the first fluid is initialized. Upon introductionof the first and second fluids, the bed of filter media expands andmoves in countercurrent flows within the vessel 20 as shown by the flowarrows in FIG. 2b . In FIG. 2 b, the filter media adjacent the first end22 of the draft tube moves toward the second end 24 in a directioncounter to the flow of wastewater during filtration. The filter media 16adjacent the second end 24 of the draft tube moves along the outside ofthe draft tube towards the first end 22 of the draft tube, therebypartially or completely rolling the bed.

Filter media moving through the draft tube mixes thereby releasing aportion of the oil and suspended solids immobilized on the filter media.Filter media exiting the draft tube may further mix in a scrub zonethereby releasing additional oil and suspended solids from the filtermedia. The oil and suspended solids are drawn from the vessel 20 viacontaminant outlet 50 in FIG. 2b . The gas is also removed from thevessel 20 via contaminant outlet 50.

The first fluid and the second fluid may continuously flow duringbackwash. Alternatively, the flow of one or both of the first and secondfluids may be intermittent. In one embodiment, air continuously flowsthrough the draft tube while water is pulsed into the peripheral zone.The pulsed flow may be periodic, in that the flow regularly cyclesbetween off and on at preselected intervals. The period of time in whichthe fluid flows may, but need not be the same as the period of time inwhich the fluid flow is interrupted. For example, the fluid may flow fora longer or shorter period of time than the period of time in whichfluid flow is interrupted. In one embodiment, the period of time inwhich the fluid flows is substantially identical to the period of timein which fluid flow is interrupted.

In another embodiment, the first fluid may be intermittently supplied tothe draft tube while the second fluid is continuously supplied duringbackwash. The second liquid is passed to the filter vessel and into thewalnut shell filter media for a first period of time in a directioncounter to the flow of the liquid through the vessel and a first liquidis passed through the walnut shell filter media in the draft tube for asecond period of time to separate at least a portion of the contaminantfrom the filter media. The duration of the first period of time may besufficient to perform a partial roll or one or more complete bed rolls.The flow of the first fluid may be interrupted while the flow of thesecond fluid continues and contaminants are removed. Flow of filtratethrough the filtrate exit may be interrupted and flow of the first fluidmay be reestablished. The flow of the first fluid may then beinterrupted while the flow of the second fluid continues to once againpartially or completely roll the bed one or more times. Again the flowof contaminants may be removed while the flow of the second fluidcontinues. The flow of the first fluid may be alternated continuouslyuntil the desired level of backwash is achieved. To complete thebackwash cycle, flow of the first fluid may be interrupted while flow ofthe second fluid continues and contaminants are removed from the vessel.Upon removal of the contaminants, the flow of the second fluid may beinterrupted and feed forward flow of wastewater may be initiated. Thecombination of pulsed backwashes may result in a partial or one or morecomplete bed rolls during backwash. In one embodiment, the bed is rolledabout 3 times. In another embodiment, the bed is rolled about 4 times.

The pulsed backwash system provides advantages over conventionalbackwash methods in that it may reduce capital and maintenance costs byeliminating mechanical equipment inside the filter vessel or outside thevessel. The pulsed backwash method may also be simpler to operate sinceit may eliminate conventional recycle pumps which remove the filtermedia from the vessel for regeneration and then return regeneratedfilter media back the vessel. Maintenance of the conventional recyclepumps is often difficult since these pumps are often located 20 to 25feet above ground. Flushing of the recycle lines once the backwash cycleis completed may also be difficult and may include manual removal of thefilter media. Furthermore, elimination of the mechanical mixers and therecycle pumps reduces system weight and footprint. Also, becausebackwash components are internal to the vessel, they may be formed ofless expensive materials, such as plastics, since they are not operatedin a pressure recycle system as are conventional external backwashcomponents. The use of lighter components may also reduce theinstallation costs in some applications, such as off shore platforms,where installation costs increase significantly with increased systemweight. Another advantage is that the gas or air used in the pulsedbackwash system may be readily available in many facilities, such asproduction gas from hydrocarbon production or refinery facilities,thereby eliminating the need for a compressor to supply the gas to thepulsed backwash system. More significantly, because the pulsed backwashsystem may utilize a gas and a liquid, it reduces the volume of backwashliquid generated. Furthermore, because the filter media is not removedfrom the vessel during backwash, it's exposure to piping and pumps isreduced so that filter media having a lower modulus of elasticity thanconventional filter media may be used. For example, black and Englishwalnut shells are known to provide superior coalescing and filtration ofwastewater containing oil, however walnut shell filters are typicallyfilled with the more expensive black walnut shells because it has ahigher modulus of elasticity than English walnut shells and thereforehas a more durable surface for use in external backwash systems. Becausebackwashes are performed internally according to one embodiment, it maybe possible to use the less expensive English walnut shell withoutsacrificing efficiency.

Once it is determined that sufficient oil and suspended solids have beenremoved from the filter media and/or the backwash has been running for apredetermined period of time, flow of the first and second fluids arethen interrupted and wastewater flow to the feed inlet is initiated asshown in FIG. 2c while the filter media sets in the bed.

FIG. 3 is a cross sectional schematic plan view of filter mediaapparatus 300 similar to filter media apparatus 200 other than filtermedia apparatus comprises four draft tubes 18 positioned in filter media16. Filter media apparatus 300 also differs from filter media 200 inthat apparatus 300 may also comprise four first fluid inlets (not shown)to direct the first fluid to each of the four draft tubes. Otherstructural features of apparatus 300 may be similar or identical tothose of filter media apparatus 200 and are therefore not shown.Filtration and backwash cycles in apparatus 300 are performed in thesame manner as with apparatus 200, other than flow to the four firstfluid inlets may be either initiated or interrupted simultaneously. Aswith apparatus 200, filter media apparatus 300 may optionally includeadditional first fluid inlets and/or second fluid inlets in theperipheral zone 26 to assist rolling the bed. The presence of multipledraft tubes within the filter media may more uniformly distribute thegas exiting the draft tubes and entering the scrub zone, therebyincreasing turbulence in the mixing scrub zone for more effectiveremoval of the oil and suspended solids from the filter media. Theelimination of a central draft tube as shown in FIG. 3, though notnecessary, may allow for easier and more versatile water distribution.

FIG. 4 is a schematic drawing of filter media apparatus 400. Filtermedia apparatus 400 is similar to filter media apparatus with theexception that the draft tube 18 of apparatus 400 includes a baffle 62.A baffle may be advantageous when a diameter of the backwash tube issufficiently large so as to have the potential for back mixing to occurwithin the draft tube. Back mixing of the wastewater and filter mediawithin the draft tube may negatively impact the flow and mixing of thefilter media in the draft tube resulting in poor suction at the firstend of the draft tube and reducing the filter media rolling efficiency.The baffle may be sized and shaped for a particular purpose. FIG. 4shows a cylindrical baffle 62 centrally positioned within the draft tube18. Although one draft tube is shown, it is understood that any numberand configuration of draft tubes may be used so long as the draft tubesystem provides the desired volume of media rolling through the vessel.

In apparatus 400, the first fluid inlet 34, such as a gas inlet, may beconstructed and arranged to direct air though the entire draft tubeincluding an outer portion 66 bounded by the sidewall of the draft tubeand the sidewall of the baffles, as well as though a central portion 64of the draft tube bounded by the sidewall of baffle 62. The outer region66 may be an annular region surrounding the cylindrical draft tube andcylindrical baffle. Filtration and backwash cycles in apparatus 400 areperformed in the same manner as with apparatus 200. As with apparatus200, filter media apparatus 400 may optionally include additional firstfluid inlets and/or second fluid inlets in the peripheral zone 26 toassist rolling the bed. During backwash, the filter media flows throughthe central portion 64 as well as the outer region 66, while the filtermedia in the peripheral zone flows in a counter current direction.During feed forward filtration, the liquid containing contaminant flowsthrough the filter media positioned in the peripheral zone 26, the outerregion 66 and the central portion 64.

FIG. 5 is an elevated schematic view of one embodiment of a base portion500 of a draft tube 518 suitable for use in any of filter media units200, 300, 400. In this embodiment draft tube 518 comprises a pluralityof passageways 570 in the first end 522 of the draft tube. The cut outsmay assist the flow of filter media from the peripheral zone (not shown)to the first end 522 and through the draft tube 518. The passageways maybe identical to one another and regularly spaced about the second end ofthe draft tube to provide consistent flow within the draft tube. Thepassageways 570 may have any size and shape to allow sufficient flow ofthe filter media and backwash fluid within the draft tube to provide adesired backwash cycle.

FIG. 6 is a block diagram of wastewater treatment system 600 comprisinga first filter media apparatus 610 and a second filter media apparatus620 operating in parallel. Filter media units 610 and 620 may comprise avessel, a filter media, and a draft tube positioned within the media. Asource of wastewater 630 containing oil and suspended solids is fluidlyconnected to a wastewater feed inlet of filter media apparatus 610 viavalve 632. Similarly the source of wastewater 630 is fluidly connectedto a wastewater feed inlet of filter media apparatus 620 via valve 634.The source of wastewater is fluidly connected to a second fluid inlet ofapparatus 610 via valve 636, and is also fluidly connected to a secondfluid inlet of apparatus 620 via valve 638.

A source of gas 640, such as an air blower, is fluidly connected to agas inlet to apparatus 610 via valve 646. The source of the gas 640 isalso fluidly connected to a gas inlet of apparatus 620 via valve 648.

While apparatus 610 is running in a filtration cycle, valve 632 is opento supply wastewater to the apparatus. Accordingly, valves 636, 646 areclosed to prevent backwash of the bed with the wastewater and the gas,respectively.

Apparatus 620 may be operating in a backwash cycle for all or a portionof the time that apparatus 610 is operating in the filtration cycle.While apparatus 620 is operating in the backwash cycle, valve 634 isclosed to prevent wastewater from entering the feed inlet of theapparatus. Valves 638, 648 are open to provide wastewater and gas to thebackwash cycle. In the system of FIG. 6, controller 650 may respond to asignal generated by a timer indicating a predetermined backwash periodhas elapsed and generate one or more control signals to cause valves638, 648 to close and valve 634 to open so that apparatus 620 mayoperate under filtration conditions.

Optionally, a source of filtrate may be fluidly connected to the secondfluid inlet of the first apparatus and to the second fluid inlet of thesecond apparatus. In another embodiment, the second fluid may beconnected to the first and second filtrate outlets to provide the secondfluid to the first apparatus and the second apparatus, therebyeliminating separate second fluid inlets.

In the system of FIG. 6, controller 650 may also respond to signals fromsensors (not shown) positioned at any particular location within thesystem. For example, a sensor in filter media apparatus 610 operating inthe filtration cycle may generate a signal indicating that the pressuredrop across the filter media bed has reached a predetermined value atwhich it may be desirable to perform a backwash of the media inapparatus 610. The controller 650 may respond by generating one or morecontrol signals to close valve 632 and open valves 636, 646 to start thebackwash cycle. The controller 650 may then receive and respond tosignals by alternatively place one or both units 610, 620 in service ortake one or the other out of service to run a backwash cycle.

During the backwash cycles of either apparatus 610, 620, controller 650may signal valves 636, 638, 646, 648 to remain continuously open or toopen and close intermittently to pulse the backwash. During theswitchover of each bed from the backwash cycle, controller 650 may alsointermittently open and close valve 646, 648 to provide pulses of gas tothe draft tube to aid in setting the bed. A pulse of gas through thedraft tube may disturb the bed after which the bed gravity settles. Apulse of gas may then again be directed through the draft tube to againdisturb the bed after which the bed gravity settles. The pulsed bedsetting may continue for a predetermined period of time or pulses, oruntil the bed has settled to a desired height, at which time the valves646, 648 may remain closed as forward feed of the source of wastewater630 is initiated. During pulsed bed settling with gas, a liquid may, butneed not, be pulsed into the vessel via valves 636, 638 to assistsettling. Pulsing the liquid may occur between or at the same time asthe gas pulses to settle the bed.

FIG. 8 is a flow chart illustrating an embodiment of the invention. InFIG. 8, step 801 includes passing a feed liquid to a filter apparatus.Filtrate is removed during feed forward filtration of step 801. Whilepassing the feed liquid, a sensor monitors pressure in first filterapparatus to determine if the pressure drop across the filter media hasreached a predetermined value shown in step 802. If the value of thepressure drop has not reached the predetermined value, liquid feedcontinues to pass through the first filer apparatus as in step 801. Ifthe pressure reading is determined to have reached or exceeded apredetermined value, the flow of feed liquid to the filter apparatus isinterrupted in step 803.

In FIG. 8, after the flow of the feed liquid is interrupted, a flow of afirst fluid is introduced into a draft tube in the vessel per step 804in a direction counter to the flow of feed liquid. A flow of a secondfluid is also introduced into a peripheral zone per step 805. In step806, a determination is made as to whether or not the filter media hasbeen sufficiently rolled. This determination may be made upon theoverall time period passing in steps 804 and 805. Per step 806, if thefilter media has been sufficiently rolled, the flow of the first fluidis interrupted in step 807. If the filter media has not beensufficiently rolled, the flow of the second fluid is interrupted in step809. After interrupting the flow of the second fluid, the flow of thesecond fluid is again initiated in step 810. Once again, a determinationis made in step 811 as to whether or not the filter media has beensufficiently rolled. If the bed has been sufficiently rolled, the flowof the first fluid is interrupted in step 807. If the filter media hasnot been sufficiently rolled, the flow of the second fluid isinterrupted in step 809. Steps 809-811 are repeated until it isdetermined in step 811 that the filter media has been sufficientlyrolled.

Once the flow of the first fluid has been interrupted in step 807 aftera determination that the filter media has been sufficiently rolled,contaminants are removed from the filter apparatus in step 812. Afterremoval of contaminants, the flow of the second fluid is interrupted instep 813 and the flow of the feed liquid to the filter apparatus isreestablished in step 814. Filtrate is again removed during feed forwardfiltration of step 814.

The function and advantages of these and other embodiments of thepresent invention will be more fully understood from the followingexamples. These examples are intended to be illustrative in nature andare not considered to be limiting the scope of the invention.

EXAMPLE I

An experiment was conducted to determine the effectiveness of a pulsedwater backwash. A test apparatus was configured with a clear plasticcolumn having a diameter of about 12 inches and a height of about 12feet. A draft tube having a diameter of about 3 inches and a height ofabout 5 feet was placed at the center of the column. An air diffuser wasattached to an air inlet at the base of the draft tube. Three nozzlesfor delivering water were equally spaced about the periphery of thecolumn. Each nozzle included an elbow to direct water tangentially inthe column. The column was filled with 66 inches of black walnut shellsso that the shell bed extended approximately 6 inches above the heightof the draft tube.

A series of tests were performed to measure the effect of air and waterflow rates during backwash. Backwash efficiency was measured in thevelocity of the walnut shells traveling down the outside of the drafttub in the peripheral zone. A portion of the walnut shells were paintedfor visual confirmation of motion during backwash. Initial resultsindicated that that by pulsing the water the generation of backwashvolume from the walnut shell filter was significantly reduced withoutsacrificing backwash efficiency.

Further tests were conducted with the above apparatus to comparecontinuously flowing backwash water to pulsing the water whilemaintaining a constant flow rate of air through the draft tube. In afirst test, the water continuously flowed into the peripheral zone at arate of about 3 GPM while in a comparative test water flow was pulsedinto the peripheral zone with a water pulse of about 6 GPM for about 1second followed by no flow for about 1 second to achieve an overall flowof 3 GPM. In a second test, the water continuously flowed into theperipheral zone at a rate of about 4 GPM while in a comparative testwater flow was pulsed into the peripheral zone with a water pulse ofabout 8 GPM for about 1 second followed by no flow for about 1 second toachieve an overall flow of about 4 GPM. The results are shown in TableI.

TABLE I Water Flow Velocity Time to Roll Rate (GPM) (in/min) Bed (min.)3 Continuous 23.5 2.8 3 Pulsed 26.4 2.5 4 Continuous 28.1 2.3 4 Pulsed34.2 1.9

As can be seen, pulsing the water increased the velocity of the walnutshells by about 12 percent and reduces the time to roll the bed by about11 percent when compared to the continuous flow rates of 3 GPM whileproducing the same volume of backwash. Similarly, pulsing the waterincreased the velocity of the walnut shells by about 21 percent andreduces the time to roll the bed by about 17 percent when compared tothe continuous flow rates of 4 GPM while producing the same volume ofbackwash.

These results indicate that pulsing the water during backwash is moreefficient so that the backwash cycle may be performed in a shorterperiod of time, generate less backwash, or a combination of both. Basedupon this data, it was estimated that the pulsed backwash would generate20-30 gallons of water per square foot of filtering area compared togenerating about 160 gallons of water per square foot of filtering areawith continuously flowing water.

EXAMPLE II

A test was conducted to determine the effectiveness of backwashing ablack walnut shell filter having multiple draft tubes in comparison to asingle draft tube. In a first test, a vessel having a diameter of 4 feethad one centrally located draft tube having a diameter of 12 inches wasfabricated. A portion of the walnut shells were painted foridentification and windows were positioned at various locations in thevessel to observe the movement of the walnut shells. In a second test, avessel having a diameter of 4 feet included 4 draft tubes each having adiameter of 6 inches was fabricated. The 4 draft tubes were equallyspaced throughout the vessel. Backwash water volume and gas volume wereidentical for both tests.

Visual results indicated that the multiple draft tube design was atleast as effective at rolling the bed as the single draft tube design,and in some instances was even more effective. Without being bound byany particular theory, the presence of multiple draft tubes moreuniformly distributes the air exiting the draft tubes and entering thescrub zone, thereby increasing turbulence in the mixing scrub zone formore effective removal of the oil and suspended solids from the filtermedia.

EXAMPLE III

A pilot test was conducted to determine the effectiveness of backwashinga black walnut shell filter having a baffle positioned in a draft tube.A filter media vessel having a diameter of 4 feet was fitted with adraft tube made from a 12 inch diameter pipe. A baffle formed from a 6inch diameter pipe was centrally located in the draft tube. Clearwindows were installed in the filter medial vessel in order to observebackwash efficiency. Visual results of the pilot test confirmed that thedraft tube with a baffle provided adequate backwash for the 4 ft largediameter vessel.

EXAMPLE IV

A test was conducted to determine the effectiveness of deliveringalternating pulses of wastewater and air to a bed of black walnut shellmedia to set the bed after a backwash cycle. Walnut shell media wasconventionally set in a vessel having a diameter of 12 inches by feedingwastewater in a forward flow to a bed depth of 60 inches. The walnutshell media was then expanded during the backwash cycle to a height of66 inches. For comparison, the bed was conventionally set back to 60inches with continuously flowing forward feed for about 5 minutes.Forward flow feed was then performed to measure the efficiency of thebed.

The walnut shell media was then again expanded to a height of 66 inchesafter which alternating pulses or short bursts of wastewater and airwere added to the walnut shell media in a reverse feed direction forabout 2 minutes and allowed to settle. Water was pulsed through the bedat a flow rate of about 1.5 gal/min for one second after which air waspulsed through the bed in a short burst for one second. The bed set to adepth of 53 inches, which is 7 inches less than the original depthresulting in a condensed bed having a reduced void volume in the filtermedia. Forward flow feed was then performed on the condensed bed todetermine the efficiency of the condensed bed compared to theconventionally set bed. The results of the total outlet oilconcentration verses time in feed forward filtration are shown in FIG.7. Linear regression equations were calculated from the data for theconventionally set bed, labeled as a loose bed, and the pulsed set bed,labeled a set bed.

TABLE II Total Oil in Total Oil in % Change Time Effluent (ppm) Effluent(ppm) in Oil in (min) Conventional Set Pulsed Set Effluent 100 19.36421.292 +10.0 200 26.984 25.512 −4.3 300 34.604 29.732 −14.1 400 42.22433.952 −19.6 500 49.844 28.172 −23.4 600 57.464 42.392 −26.2 700 65.08446.612 −28.4 800 72.704 50.832 −30.1

At seen in the tables above, as filter time increased, the pulsed setbed was significantly more effective in removing total and free oil fromthe wastewater, by as much as 30 percent at 800 minutes. Similarly thegraph also shows that as time increased the pulsed set bed removed moreoil than the conventionally set bed.

The pulsed set bed may therefore allow the walnut filter media to be runfor a longer period of time than conventionally set beds before it isdesirable to run a backwash. Extending the period of time betweenbackwash cycles may also reduce the total amount of generated backwashover the life of the media. Compacting the bed may also result in beddesigns with a smaller bed depth reducing vessel size and weight.

Having thus described several aspects of at least one embodiment of thisinvention, it is to be appreciated various alterations, modifications,and improvements will readily occur to those skilled in the art. Suchalterations, modifications, and improvements are intended to be part ofthis disclosure, and are intended to be within the spirit and scope ofthe invention. Accordingly, the foregoing description and drawings areby way of example only.

This invention is not limited in its application to the details ofconstruction and the arrangement of components set forth in thefollowing description or illustrated in the drawings. The invention iscapable of other embodiments and of being practiced or of being carriedout in various ways. Also, the phraseology and terminology used hereinis for the purpose of description and should not be regarded aslimiting. The use of “including,” “comprising,” or “having,”“containing,” “involving,” and variations thereof herein, is meant toencompass the items listed thereafter and equivalents thereof as well asadditional items. Only the transitional phrases “consisting of” and“consisting essentially of” are closed or semi-closed transitionalphrases, respectively, with respect to the claims. As used herein, theterm “plurality” refers to two or more items or components.

What is claimed is:
 1. A system for filtering wastewater comprising: asource of wastewater comprising oil and suspended solids; a filter unitcomprising: a vessel; a walnut shell filter media positioned in thevessel; a feed inlet positioned in the vessel above the walnut shellfilter media and fluidly connected to the source of wastewater via afluid line comprising a first valve for controlling flow of thewastewater into the feed inlet, the feed inlet arranged to enable flowof the wastewater through the walnut shell filter media in a firstdirection; a draft tube system positioned in the walnut shell filtermedia configured to substantially roll the walnut shell filter media,wherein the draft tube system comprises a draft tube located in thevessel defining a peripheral zone positioned between a side wall of thedraft tube and a side wall of the vessel; a first fluid inlet configuredto deliver a first fluid to the draft tube system via a fluid linehaving a second valve for controlling flow of the first fluid to thedraft tube system, the first fluid inlet arranged to enable flow of thefirst fluid into the draft tube system in a second direction oppositethe first direction; a second fluid inlet configured to deliver a secondfluid to the peripheral zone via a fluid line having a third valve forcontrolling flow of the second fluid to the peripheral zone, the secondfluid inlet also arranged to enable flow of the second fluid into theperipheral zone in the second direction opposite the first direction;and a controller in electrical communication with the first valve,second valve, and third valve and configured to generate a controlsignal that moves any one or more of the valves between an open and aclosed position to regulate flow of the wastewater, first fluid, orsecond fluid there through.
 2. The system of claim 1, further comprisinga first sensor in the first sensor in the filter unit, wherein thecontroller is configured to generate a control signal to close the firstvalve in response to a determined pressure value by the first sensor. 3.The system of claim of claim 1, wherein the first fluid comprises a gas,and wherein the second fluid comprises the wastewater.